STARTER ENGAGES WITH SHIFT LEVER AND WHEN JUST TURN KEY TO ON

1994 Jaguar XJ6 • 150,000 miles

Car would always turn over when trying to just put in neutral. Had to replace crankshaft position sensor to get running, finally got running and went to go into gear and engaged starter. Then couldn't turn key to on without starting and starter would stay engaged.

Gremlins, that's what you have. You have something grounding at the wrong time, or when it shouldn't be. In nuetral and park, you have a solid ground going to a solenoid that let's you start the car. In any other gears you don't. In your case, your ground is continuing past this point. My guess here, with your brief explanation is that the key switch is bad.